The present invention pertains to the fluid driven turbine art and, more particularly, to a cold air, dual turbine drive.
Numerous turbine configurations are known to the prior art. Turbines are commonly employed to convert a fluid flow to rotation of the drive shaft. A particular application for turbines is in the testing of fans or propellers for use in aircraft. Ideally, the propeller or fan under test should be driven at speeds normally expected in its intended application. Further, the test structure behind the fan or propeller should be aerodynamically similar to the structure encountered in the actual application, such that flow patterns past the fan or propeller can be simulated. In addition, the drive source to the fan or propeller should be sufficiently quiet such that noise levels produced by the fan or propeller can be accurately measured.
A particular need in this art has been a requirement for a drive capable of the static testing of counter-rotating shafts over a broad RPM range and with sufficient horsepower to simulate the speeds actually encountered by such propellers.
Heretofore, the drives for testing counter-rotating propellers have suffered from numerous deficiencies. For example, hot gas turbine drives have been used in propeller testing, but the size of the hot gas turbines required to drive counter-rotating propellers to realistic levels has been so large that such turbines have blocked airflow behind the fan or propeller, thereby obstructing accurate airflow measurements. In addition, hot gas turbines are noisy, tending to mask the noise from the propeller under test.
A further problem associated with hot gas turbines is that they are designed to operate within a specific RPM range and do not provide a high output for speeds "off" this range. As such, the use of hot gas turbines has proved inappropriate for testing propellers over their entire operating range.
Additionally, electric motors have been employed in propeller testing. Here, as with gas turbines the electric motors required to drive propellers to realistic levels have been so large that they, also, block airflow behind the propeller. While attempts have been made in locating the motor in an adjacent location to the test propeller with drive shafts and gearing extending in a linkage from the motor to the propeller, the losses encountered in such construction have proved intolerable, as has the cost of the linkage.
There is a long-felt need in the aircraft propeller and fan testing art, therefore, for a turbine design which exhibits a useful power output over a broad RPM operating range, which is both quiet and compact in configuration, and which is capable of driving counter-rotating propellers.